1. Field of the Invention
The present invention generally relates to integrated lithographic exposure and processing system and methods of lithographic exposure and processing.
2. Description of the Related Art
Among other things, lithographic fabrication systems are used in the manufacture of integrated circuits (ICs). In such cases, a patterning device generates a circuit pattern corresponding to an individual layer of the IC, and this pattern is then imaged or exposed onto a target portion of a substrate (e.g. silicon “wafer”) that has been coated with a layer of radiation-sensitive material (e.g. “resist”). Generally, a single wafer substrate will contain a whole network of adjacent target portions that are successively irradiated via a projection system.
To this end, complete lithographic fabrication systems, such as lithographic system 100 depicted in FIG. 1A, typically employ three separate functional entities: (a) a lithographic exposure apparatus 102 that patterns the wafer substrate; (b) a wafer handling apparatus 103 that transports the wafer substrate; and (c) a separate wafer track apparatus 104 that interconnects a host of processing modules 104al-104k#, which are configured to perform various processes before and/or after the pattern is exposed onto the wafer substrate.
The term “patterning device” as employed herein should be broadly interpreted to refer to devices that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate. The term “light valve” may also be used in this context. Generally, the pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). Examples of such patterning device include:                (a) a mask: the concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the support structure will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired;        (b) a programmable mirror array: an example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that (for example) addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the said undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; in this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed using suitable electronic devices. More information on such mirror arrays can be gleaned, for example, from U.S. Pat. Nos. 5,296,891 and U.S. Pat. No. 5,523,193, which are incorporated herein by reference. In the case of a programmable mirror array, the said support structure may be embodied as a frame or table, for example, which may be fixed or movable as required; and        (c) a programmable LCD array: an example of such a construction is given in U.S. Pat. No. 5,229,872, which is incorporated herein by reference. As above, the support structure in this case may be embodied as a frame or table, for example, which may be fixed or movable as required.        
For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table; however, the general principles discussed in such instances should be seen in the broader context of the patterning device as set forth above. Also, the projection system may hereinafter be referred to as the “lens”; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a “lens”.
FIG. 1B provides a more detailed illustration of lithographic apparatus 102. As indicated in FIG. 1B, lithographic apparatus 102 comprises:                an illumination system: illuminator IL for providing a projection beam PB of radiation (e.g. UV radiation or other radiation);        a first support structure: (e.g. a mask table, mask holder) MT for supporting patterning devices (e.g. a mask or reticle) MA and connected to first positioning mechanism PM for accurately positioning the patterning device with respect to item PL;        a substrate table: (e.g. a wafer table, wafer holder) WT for holding a wafer substrate (e.g. a resist-coated wafer) W and connected to second positioning mechanism PW for accurately positioning the substrate W with respect to item PL; and        a projection system: (e.g. a refractive projection lens) PL for imaging a pattern imparted to the projection beam PB by patterning device MA onto a target portion C (e.g. comprising one or more dies) of substrate W.        
The illuminator IL receives a beam of radiation from a radiation source SO. The source SO and lithographic apparatus 102 maybe separate entities, such as when the source SO is an excimer laser. In such cases, source SO is not considered to form part of lithographic apparatus 102 and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases, the source SO may be integral part of apparatus 102, such as when the source SO is a mercury lamp. The source SO and illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.
The illuminator IL may comprise adjusting mechanism AM for adjusting the angular intensity distribution of the beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL generally comprises various other components, such as an integrator IN and a condenser CO. The illuminator provides a conditioned beam of radiation, referred to as the projection beam PB, having a desired uniformity and intensity distribution in its cross-section.
The projection beam PB is incident on the mask MA, which is held on the mask table MT. Having traversed the mask MA, the projection beam PB passes through the lens PL, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioning mechanism PW and position sensor IF (e.g. an interferometric device), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the beam PB. Similarly, the first positioning mechanism PM and another position sensor (which is not explicitly depicted in FIG. 1B 1) can be used to accurately position the mask MA with respect to the path of the beam PB, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the object tables MT and WT will be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the positioning mechanism PM and PW. However, in the case of a stepper (as opposed to a scanner), the mask table MT may be connected to a short stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.
Lithographic apparatus 102 can be used in the following preferred modes:                step mode: the mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the projection beam is projected onto a target portion C in one sweep (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.        scan mode: the mask table MT and the substrate table WT are scanned synchronously while a pattern imparted to the projection beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the mask table MT is determined by the (de-)magnification and image reversal characteristics of the projection system PL. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion.        other mode: the mask table MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the projection beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.        
Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed by lithographic apparatus 102.
As noted above, lithographic apparatus 102 also contains an exposure tool controller 102A that communicates with and controls the various mechanisms and features of the apparatus 102 described above in order to process and expose the target portion C of the wafer substrates W in the desired manner.
In current lithographic exposure apparatuses, employing patterning by a mask MA on a mask table MT, a distinction can be made between two different types of machines. In one type of lithographic exposure apparatus—commonly referred to as a wafer stepper—each target portion is irradiated by exposing the entire mask pattern onto the target portion C in one go. In an alternative apparatus—commonly referred to as a step-and-scan apparatus—each target portion C is irradiated by progressively scanning the mask pattern under the projection beam PB in a given reference direction (e.g., “scanning” direction) while synchronously scanning the substrate table WT parallel or anti-parallel to this direction. Because, in general, the projection system will have a magnification factor M (generally <1), the speed V at which the substrate table WT is scanned will be a factor M times that at which the mask table MT is scanned. More information with regard to lithographic devices as here described can be gleaned, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference.
It is to be noted that the lithographic exposure apparatus may also be of a type having two or more substrate tables (and/or two or more mask tables). In such “multiple stage” devices, the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Twin stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO 98/40791, incorporated herein by reference.
Regardless of the lithographic exposure apparatus used, the wafer substrates W may, as noted above, be subjected to a variety of processes before the pattern is exposed onto the wafer substrate. For example, wafer substrate W may be subjected to cleaning, etching, ion implantation (e.g., doping), metallization, oxidation, chemo-mechanical polishing, priming, antireflective coating, resist coating, soft bake processes, and measurement processes. These processes may be completed in individual apparatus or grouped into a common apparatus, such as select ones of the depicted processing modules 104al-104k# of wafer track apparatus 104. For example, wafer track apparatus 104 typically performs priming, antireflective coating, resist coating, soft bake, and measurement processes prior to the exposure process.
The wafer substrates W may also be subjected to a host of post-exposure processes, such as, for example, post exposure bake (PEB), development, hard bake, etching, ion implantation (e.g., doping), metallization, oxidation, chemo-mechanical polishing, cleaning, and measurement processes. Again, these processes may be completed in individual apparatus, or grouped into a common apparatus, such as select ones of the depicted processing modules 104a1-104k# of wafer track apparatus 104. For example, wafer track apparatus 104 typically performs post exposure bake (PEB), development, and measurement processes after the exposure processes. If several layers for each wafer substrate W are required, which is usually the case, the entire procedure, or variants thereof, will have to be repeated for each new layer.
As indicated above, these pre- and post-exposure processes are performed by stations or modules designed for their respective purposes. Select ones of processing modules 104al-104k# may be configured as pre-exposure processing modules, which perform pre-exposure processes, and post-exposure processing modules, which perform post-exposure processes.
The wafer substrates W are subjected to processing modules 104al-104k#, as well as the lithographic exposure apparatus 102 in a pre-defined sequence. In this arrangement, the wafer substrates W travel along a pre-specified processing path within wafer track apparatus 104 to get serviced by specific processing modules that can be tracked. Wafer track apparatus 104 contains a track controller 104A to control the specific processing path of each wafer substrate.
Wafer track apparatus 104 is coupled to wafer handling apparatus 103. Wafer handling apparatus 103 transports wafer substrates between lithographic exposure apparatus 102 and wafer track apparatus 104. Wafer handling apparatus 103 may include robotic, conveyor, or track mechanisms or combinations therefrom, to transport the wafer substrates between lithographic exposure apparatus 102 and wafer track apparatus 104. Wafer handling apparatus 103 may also include an interface section 103A to provide limited communications between lithographic exposure apparatus 102 and wafer track apparatus 104. Generally, such communications are minimal and are limited to an indication that wafer substrate W is ready to be picked up from the wafer track 104 and delivered to the exposure apparatus, or that a wafer W is ready to be picked up from the exposure apparatus 102 and delivered to wafer track apparatus 104.
Upon receiving the wafer substrate W from the wafer handling apparatus 103, exposure apparatus 102 transports the substrate W through a number of processes modules as specified by the exposure controller 102A of exposure apparatus 102. The wafer track apparatus 104, prior to delivering the substrate W to the wafer handler 103 or upon receiving the substrates from the wafer handler 103, transports the substrates W through various processing modules 104al-104k# specified by the track controller 104A of wafer track apparatus 104.
Needless to say, it is important that the features and profile of the pattern exposed on the target field C of the wafer substrate W layer are replicated as accurately as possible. To this end, manufacturers normally specify key attributes, which can be collectively considered the critical dimension (CD) of the exposed pattern, in order to characterize the features and profile of the pattern and establish a benchmark level of quality and uniformity. The CD metric may include, for example, the gap between features, X and/or Y diameter of holes and/or posts, ellipticity of holes and/or posts, area of feature, feature sidewall angle, width at the top of a feature, width at the middle of a feature, width at the bottom of a feature, and line edge roughness.
There are, however, numerous activities during the lithographic fabrication process that affect the critical dimension uniformity (CDU) and compromise the quality of the exposed pattern. Indeed, many of the very processes that service and treat the substrate wafers along wafer track apparatus 104, such as, for example, the post exposure bake (PEB), chill, and develop processing modules, contribute to variations in the CDU. Such variations may occur across a target field C, across a wafer W, and between wafers W.
Moreover, these variations may be exacerbated by the lack of communications and control between the distinct functional entities of lithographic fabrication lithographic system 100. That is, unwanted variations and non-uniformities may result from the lack of communications, timing, and control as the wafer substrates W travel to and/or from exposure apparatus 102, wafer handling apparatus 103, and wafer track apparatus 104, which houses the processing modules 104al-104k# that treat the substrates W. Ultimately these variations and non-uniformities result in the loss of yield for the lithographic fabrication process, and frequently result in decreased throughput.